This invention relates to angioplasty as a means of treating arterioscleorosis of coronary arteries. More particularly, the invention relates to a radioactive stent capable of preventing restenosis of blood vessels and a process for producing it.
Stated more specifically, the present invention relates to a radioactive cylindrical stent that has been ion injected with .sup.133 Xe and which will later emit .beta.-rays, .gamma.-rays and internal conversion electrons ejected by .gamma.-decay. The invention also relates to a process for producing the stent. The radioactive stent of the invention is placed within a blood vessel and prevents its restenosis by inhibiting abnormal growth of the smooth muscular cells in it. The advantage of the .sup.133 Xe radioactive stent of the invention is not limited to preventing blockage recurrence after angioplasy with a balloon or an ordinary non-radioactive stent; it can also replace the balloons and ordinary non-radioactive stents commonly used in angioplasy.
To treat arteriosclerosis of coronary arteries, angioplasy is performed using balloons and stents; however, postoperative stenoses often occur and the frequency is 30 -40% in the case of using balloons and 10-30% with stents. Opened blood vessels are believed to occlude mainly from abnormal growth of smooth muscular cells and it has recently been found that intravascular exposure to radiations is an effective way to prevent postoperative restenoses (Waksman R. et al., Circulation, 91, (1995) 1533-1539).
One of the ways to implement the intravascular exposure to radiations is by using a stent that has been rendered radioactive on its own and this technique is gaining increasing attention from researchers. However, the only case that has been reported on radioactive stents that are prepared by ion injection is about a .beta.-emitting radioactive stent that has been ion injected with .sup.32 p (Hehrlein C. et al., Circulation, 93, (1996) 641-645).
A problem with this prior art technique is that due to the comparatively long half-life (14.3 days) of .sup.32 p, the time of exposure to the emitted .beta.-rays is unduly prolonged to interfere with the regeneration of vascular endothelia, potentially inducing thrombus formation. Therefore, it is necessary to develop a stent that has been rendered radioactive by means of a shorter-lived radioisotope and which is capable of preventing restenosis of blood vessels without interfering with the regeneration of vascular endothelia.
In addition, in view of the fact that restenosis of a blood vessel occurs in that area of the vessel which is in contact with any surface of the inserted stent, it is required that the entire surface of the stent be uniformly ion injected with a radioactive isotope. Considering the number of patients with arteriosclerosis who are currently under treatment, mass production of radioactive stents is also an important factor.